Lewis Acid-Enabled Chemodivergent Cycloadditions of Donor–Acceptor Cyclopropanes with Indoline-2-Thiones

Abstract

Lewis acid-enabled reactions of donor–acceptor cyclopropanes (DACs) with indoline-2-thiones are reported. The reaction exhibits tunable annulation depending on the Lewis acid and the substituent at N1 of the indoline-2-thiones. With AlCl₃ as the Lewis acid and 1-isopropylindoline-2-thiones as reactants, a direct ring opening with DACs, followed by intramolecular nucleophilic addition/dehydration takes place leading to the formation of dihydro-2H-thiepino[2,3-b]indoles in moderate to good yields. Using Yb(OTf)₃ as promoter and 1-unsubstituted indoline-2-thiones as reactants, a (3 + 2) cycloaddition with DACs accompanied by sulfur rearrangement nucleophilic addition/dehydration takes place to give 3-indolyl-4,5-dihydrothiophenes in moderate yields. In addition, the synthetic transformation of 3-indolyl-4,5-dihydrothiophene to sulfone and indole-based axially chiral scaffolds further extends the synthetic utility and structural complexity.